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Answer Key: Practice Worksheet – G9 – Term3 True/False Indicate whether the statement is true or false. T 1. Energy doesn't have to involve motion. T 2. Energy is the ability to cause change. T 3. Energy is measured in joules. T 4. When you ride a playground swing, your potential energy is greatest at the highest point. F 5. Chemical(radiant) energy travels from the Sun to Earth and is transformed into light energy by plants. F 6. As mass decreases, kinetic energy increases. T 7. Lowering an object decreases its potential energy. T 8. In a car engine, burning fuel produces heat, which causes gases to expand, producing kinetic energy. F 9. The sum of potential and kinetic energy in a system is called the total(mechanical) energy. T 10. Carbohydrates and fats provide our bodies with energy in the form of calories. T 11. Energy from the Sun and energy from food are just different forms of the same thing. T 12. In order for work to be done on a object, the object must move. F 13. Conduction is the transfer of energy by the bulk movement of matter. F 14. Radiation is the transfer of energy in the form of particles. T 15. In a forced-air heating system, the warm air circulates by convection. T 16. Winds are examples of convection currents. F 17. Shiny materials absorb(reflect) radiant energy. F 18. Heat(temperature) is a measure of the average kinetic energy of all the particles in an object. T 19. When you bring the south ends of two magnets close together, they repel each other. T 20. Paper clips and other objects that contain iron can become temporary magnets. Modified True/False Indicate whether the statement is true or false. If false, change the identified word or phrase to make the statement true. F 21. Energy in the form of motion is potential energy. ____kinetic___ T 22. According to the law of conservation of energy, mechanical energy can be changed to heat energy. ____________________________ F 23. A rock at the edge of a cliff has kinetic energy because of its position. _potential_ T 24. When you put on the brakes of a bicycle, friction causes some of the mechanical energy to change to thermal energy. _________________________ F 25. According to the law of conservation of energy, energy can be created or destroyed. Can’t F 26. Energy that is stored is kinetic energy. __potential__ T 27. Energy stored in food you eat is chemical potential energy. _________________________ F 28. Elastic energy is the total potential and kinetic energy in a system. mechanical_ T 29. Energy is measured in joules. _________________________ F 30. Compression energy is stored in a stretched rubber band. _elastic potential_ T 31. A book sitting on a shelf has gravitational potential energy. ___________________ F 32. Power is work done over a distance. ___time____ F 33. Friction changes the useful work of a machine into mechanical energy. _thermal_ F 34. A conductor is a material that doesn't allow electrons to flow through it easily. insulator T 35. The presence of a static electric charge can be detected by an electroscope. F 36.A lightning bolt occurs when billions of protons are transferred at the same time. electrons F 37. Thunder produces air temperatures hotter than the Sun's surface. lightning T 38. The rearrangement of electrons on a neutral object caused by a nearby charged object is called charging by induction. _________________________ F 39. Voltage difference is measured in amperes. ___volts____ F 40. The unit used to measure current is the volt. ___Amperes______ Multiple Choice Identify the choice that best completes the statement or answers the question. ____41.The kinetic energy of an object increases as its ____ increases. a. gravitational energy c. specific heat b. potential energy d. velocity ____42.Increasing the speed of an object ____ its potential energy. a. does not affect c. decreases b. increases d. changes ____43.The SI unit for energy is the ____. a. calorie b. joule c. d. meter per second kilogram ____44.You can calculate kinetic energy by using the equation ____. a. KE (J) = m (kg) 9.8 m/s2 h (m) c. KE (J) = 1/2 m (kg) v2 (m2/s2) b. KE (J) = w (m) h (m) d. KE (J) = 9.8 m/s2 1/2 m (kg) ____45.You can calculate gravitational potential energy by using the equation ____. a. c. GPE (J) = h (m) 9.8 m/s2 GPE (J) = 1/2m (kg) 1/2h (m) 2 b. d. GPE (J) = 1/2h (m) w (m) GPE (J) = m (kg) 9.8 m/s h (m) ____46.A bus engine transfers chemical potential energy into ____ so that the bus moves. a. thermal energy c. electrical energy b. gravitational potential energy d. kinetic energy ____47.In a nuclear fusion reaction, mass is transformed into ____. a. matter c. energy b. nuclei d. light ____48.According to the law of conservation of energy, the total amount of energy in the universe ____. a. remains constant c. increases b. changes constantly d. decreases ____49.If a weight lifter is holding barbells above his head, what does he have to do to perform work? a. stand still c. step forward b. move barbells sideways d. lower barbells ____50.The rate at which work is done is called ____. a. efficiency b. effort time c. d. force power ____51.The unit of power is the ____. a. joule b. watt c. d. m/s second ____52.A material that reduces the flow of heat by conduction, convection, and radiation is ____. a. a conductor c. an insulator b. condensation d. a solar collector ____53.All of the following are good conductors of heat EXCEPT ____. a. air c. copper b. aluminum d. silver ____54.The transfer of energy that does NOT require matter is ____. a. combustion c. conduction b. radiation d. convection ____55.Energy from the Sun travels to Earth as ____. a. chemical energy b. combustion c. d. radiant energy mechanical energy ____56.The inside surface of the glass inside a vacuum bottle is coated with aluminum to prevent heat loss by ____. a. combustion c. conduction b. radiation d. convection ____57.A device that converts thermal energy into mechanical energy is a ____. a. conductor c. heat engine b. refrigerator d. heat mover ____58.Through which of the following will convection most likely occur? a. liquids and gases c. solids b. solids and liquids d. solids and gases ____59.Which of the following would be the best insulator? a. air b. aluminum c. d. copper silver ____60.Electric charge that has accumulated on an object is referred to as ____. a. circuit electricity c. current electricity b. current circuit d. static electricity ____61.A static discharge differs from an electric current in that a static discharge ____. a. involves the movement of ions as well as electrons b. is a flow of electrons c. lasts for only a fraction of a second d. results because a force is exerted on the electrons ____62.A material through which electrons do NOT easily flow is a(n) ____. a. conductor c. insulator b. fuse d. transformer ____63.If the leaves of an electroscope spread apart, it indicates that ____. a. the leaves of the electroscope are neutral b. the leaves of the electroscope have received a charge c. no charge is moving through the electroscope d. there is static electricity in the electroscope ____64.Lightning is ____. a. a buildup of neutrons b. harmless c. d. a high-voltage electric current a large discharge of static electricity ____65.Which of the following is the correct relationship among power, current, and voltage? a. P = I/V c. P = I V b. V = P I d. E = P t ____66.The location of the strongest magnetic forces is the ____. a. electromagnets c. b. magnetic domains d. magnetic fields magnetic poles ____67.The region around a magnet where the magnetic forces act is the ____. a. electromagnetic pole c. magnetic field b. magnetic domain d. magnetic pole ____68.Objects that keep their magnetic properties for a long time are called ____. a. electromagnets c. permanent magnets b. magnetic domains d. temporary magnets ____69.The current that flows in an electric circuit carries ____. a. chemical energy c. b. mechanical energy d. ____70.The atoms in a magnet are ____. a. arranged randomly b. aligned according to magnetic fields ____71.The magnetic force of a magnet is ____. a. the same at all parts of the magnet b. strongest at the center thermal energy electrical energy c. d. negatively charged positively charged c. d. strongest at the poles weakest at the poles ____72.The theoretical point at which all molecular motion stops is called ____. a. the boiling point c. the melting point b. absolute zero d. the frozen point ____73.According to ____, the buoyant force on an object in a fluid is equal to the weight of the fluid displaced by the object. a. Bernoulli’s principle c. Charles’s law b. Boyle’s law d. Archimedes’ principle ____74.Whether an object will sink or float in a fluid is determined by ____. a. Bernoulli’s principle c. Charles’s law b. Boyle’s law d. Archimedes’ principle ____75.The magnetic field that surrounds a magnet exerts a. electrical current b. air pressure c. d. the magnetic force resistance ____76.Which of the following elements is magnetic? a. aluminum b. iron c. d. tin lead ____77.The interaction between two magnets is called: a. a magnetic force b. a magnetic field c. d. polarity current ____78.Groups of atoms with aligned magnetic poles are called a. magnetic domains c. b. magnetic fields d. elements permanent magnets ____79.Iron is a magnetic material, but an iron nail does not behave like a magnet because _______ . a. its magnetic domains are aligned c. its magnetic domains are arranged randomly b. it contains too few magnetic d. the atoms in the iron exert a force domains on all the other atoms ____80.Electrical power is expressed in __________. a. amperes b. volts ____81.Electric charges flow from __________. a. low-voltage areas to high-voltage areas b. insulators to conductors ____82.__________ is the push that causes charges to move. a. voltage difference b. electric current c. d. ohms watts c. low-resistance areas to highresistance areas high-voltage areas to low-voltage areas d. c. d. electric power resistance Completion Complete each statement. 83. If an object has energy, this means that the object has the ability to cause _change_. 84. If you double the velocity of an object, you increase its kinetic energy by a factor of _4 times_. 85. Stored energy is called _potential_ energy. 86. A fire warms you by transferring _radiation_ energy. 87. On a swing your potential and kinetic energies change, but your mechanical energy does not. 88. According to the law of conservation of energy, energy can change form, but it cannot be created or destroyed under ordinary conditions. 89. When you move your hand or foot, your body has converted potential energy into kinetic energy. 90. You can determine how much energy various foods can give you by checking their calorie content. 91. Work, like energy, is measured in __joules____. 92. Good _insulator_ do not allow heat to move easily through them. 93. All heating systems must have a source of energy in order to produce heat. 94. Thermal energy is the total energy of the molecules in a material. Figure 6-1 95. In Figure 6-1, thermal energy is transferred to the sunbather in room B primarily by radiation. 96. In Figure 6-1, most of the heat provided by the fireplace in room C goes up the chimney and is therefore transferred by convection. 97. In Figure 6-1, the thermal energy of the iron in room D is transferred to the clothes by conduction. 98. In Figure 6-1, room A, the heat from the pot on the stove moves to the pot's handle by conduction. 99. The SI unit of pressure is the Pascal. Matching a. energy b. buoyant force c. kinetic energy d. potential energy e. gravitational potential energy f. elastic potential energy g. chemical potential energy h. work i. temperature j. thermal energy k. heat l. transferring heat by conduction m. transferring heat by convection n. o. p. q. r. s. t. u. v. w. x. y. z. transferring heat by radiation heat conductors heat insulators static electricity electric field electric conductor electric insulator charging by conduction (contact) charging by induction grounding voltage difference electric current pressure z 100. force per unit area y x w v u t 101. the net flow of charge in one direction s r q p o n m 107. a material where electrons move easily l 114. transfer of heat by collisions of particles in matter k j i h g f e d c b a 115. thermal energy that flows from higher temperature to lower temperature 102. the force that causes charges to flow 103. connecting an object to Earth by a conductor 104. rearrangement of charge on a neutral object by a nearby charged object 105. the process of transferring charge by rubbing or touching 106. a material where electrons cannot move easily 108. area around the charge where it exerts force on other charges 109. accumulation of excess electric charge 110. materials that don’t allow heat to pass through them easily 111. materials that allow heat to pass through them easily 112. transfer of heat by electromagnetic waves 113. transfer of heat by movement of warm and cold fluids 116. the sum of kinetic and potential energy of all particles 117. a measure of the average kinetic energy of all particles 118. the transfer of energy when a force moves an object 119. energy stored in chemical bonds 120. energy stored in materials that can be compressed or stretched 121. energy stored due to position 122. stored energy 123. motion energy 124. is equal to the weight of the displaced fluid 125. ability to cause change Problems: Section 4.1 1. Two bullets have the mass of 3 g and 6 g, respectively. Both are fired with a speed of 40 m/s. Which bullet has more kinetic energy? KE = ½ m v2 Bullet (1) Bullet (2) KE= (0.5)(3/1000)(40)2 KE = (0.5)(6/1000)(40)2 = 2.4 J 2. = 4.8 J (more KE) A spoon is raised 21 cm above a table. If the spoon and its contents have a mass of 30 g, what is the gravitational potential energy associated with the spoon at that height relative to the table? GPE = m g h = (30/1000) (9.8) (21/100) = 0.06 J 3. What is the speed of a 55 kg woman running with a kinetic energy of 412.7 J? KE = ½ m v2 v2 = v= 4. 15.007 = 3.87 m/s A carpenter lifts a 10-kg piece of wood to his shoulder 1.5 m above the ground. He then sets the wood on his truck at 1.0 m above the ground and makes his delivery going 10 m/s. a) What is the wood’s potential energy on the carpenter’s shoulder? b) On the truck? c) What is the wood’s kinetic energy during the delivery? d) What is the wood’s mechanical energy during the delivery? a) Answer: GPE (on shoulder) = m g h = 10 x 9.8 x 1.5 = 147 J b) Answer: GPE (on truck) = m g h = 10 x 9.8 x 1 = 98 J c) Answer: KE = (½) (m) (v2) = (0.5)(10)(10)2 = 500 J d) Answer: Mechanical energy = KE + GPE (truck) = 500+98= 598J 5. Missy Diwater, the former platform diver for the Ringling Brother's Circus, had a kinetic energy of 12 000 J just prior to hitting the bucket of water. If Missy's mass is 40 kg, then what is her speed? KE = ½ m v2 v2 = 600 v = 24.5 m/s 6. A car moving at a speed of 20 m/s has a kinetic energy of 300 000 J. What is the car’s mass? m= 7. 1500 kg A box with a mass of 14.8 Kg sits on the floor. How high would you have to lift the box to for it to have a gravitational potential energy of 355 J? h= Section 16.2 1. A floating object displaces 0.6 m3 of water. Calculate the buoyant force on the object and the weight of the object. (the density of water is 1000 Kg/m3) Floating means FB = Weight So: Weight = 5880 N 2. A block of wood of mass 3.5 kg floats in water. Calculate the buoyant force on the block. FB = mf g = (3.5) (9.8) = 34.3 N 3. The pressure of a gas contained in a cylinder with a movable piston is 300 Pa. The area of the piston is 0.5 m2. Calculate the force that is exerted on the piston. F = P A = (300) (0.5) = 150 N 4. A snowboard, with 0.5 m2 area, exerts a pressure of 120 Pa on the snow. What is the snowboard weight? Weight = F = P A = (120)(0.5) = 60 N 5. A cube of steel that measures 5.0 cm on each side is immersed in water. The density of water is 1000 kg/m3. What is the buoyant force acting on the cube? Why? Vf = 5 x 5 x 5 = 125 cm3 5cm 6. Consider that: of water = 1000 kg/m3 and that g = 10 m/s2 a) Calculate the buoyant force. FB = W – W’ = 24 – 20 = 4 N b) Calculate the volume of the immersed object. Section 5.1 1. 2. At a tractor pull, one machine has a run that produces 28,000 Joules in 2 seconds. How many Watts of power did this tractor produce? How many minutes does it take a machine with a power of 2100 W to do 700 joules of work? = 0.3 s The question wants the time in minutes = 0.360 = 5x10-3min 3. How much work is done by a 125 watt blender that is crushing ice for 5 minutes? Work = power x time (seconds) = 125 x (5x60) = 37500 J Section 6.1 1. Convert each of the following: a. -20 C= 253 K b. 100C = 212F c. 80 F= 299.7 K d. If someone says that the temperature will be 303 K today, how can you express that temperature in °C and °F? Step 1: change Kelvin to Celsius: C=K-273 = 303-273= 30 °C Celsius = 30 °C Step 2: change Celsius to Fahrenheit: °F=9/5 °C + 32 = [9/5 x 30]+32= 86 °F Fahrenheit = 86 °F Section 7.2 1. A flashlight bulb uses 2.4 W of power when the current in the bulb is 0.8 A. What is the voltage difference supplied by the batteries? 2. If we connect a 120V supply to a 60W bulb, what current would flow in the circuit? 3. A 110-volt toaster oven draws a current of 6 amps on its highest setting as it converted electrical energy into thermal energy. What is the toaster's maximum power rating?